An ongoing controversy in the field of pulmonary physiology is the origin of the lung sounds that are heard on the chest wall. The origin of the so-called vesicular lung sound has been placed in the upper airway, alveoli and in between by different investigators. Preliminary studies done in this lab strongly suggest that the inspiratory component of the vesticular sound is produced within the airways of the lung, and that the expiratory component is produced, at least in part, above the main carina. Furthermore, when the relative location of the inspiratory component of the vesicular sound is plotted against the maximal mid-expiratory flow rate of a forced vital capacity, there appears to be alinear, inverse relationship between them; implying a shift of the origin of this sound toward the chest wall that is proportional to the degree of obstruction. In order to confirm this relationship and determine whether it will be of value in the detection of airways obstruction by lung sound analysis, a larger group of patients, with varying degrees of obstruction, need to be studied with more complete determinations of pulmonary function. The method used here to determine the relative distance from the chest wall of the lung sound in question is to record the sound with two microphones separated by a fixed distance. The two signals are then mixed together after phase inverting one of them and the amplitude measured. Sounds originating far from the microphones will tend to be detected by both of them and result in amplitude cancellation after mixing. Those sounds originating close to the microphones will be detected by one or the other primarily and result in less cancellation or none at all.